Irrigation tape and method of producing same

ABSTRACT

A drip irrigation tape and a method and apparatus for manufacture of same in which there are foils of thermoplastics material formed and sealed to produce a main waterway extending along the tape, and a series of tortuous flow restricting channels which are formed in a further foil by forming these in a channel shape mould on a drum, each channel communicating at one position with the waterway and having an outlet at another position to give a drip feed from each channel, the invention further including using an extrusion of thermoplastics foil directly from an extruding machine into such a forming machine, effecting an aperture from the tortuous channel to the main waterway by using a heated finger, effecting an outlet from the tortuous channel by providing an offset channel part which can then be nicked with a hot blade, and effecting an improved sealing together by using spaced apart dimples in providing joining fusing pressure.

This invention relates to an irrigation tape of the general type inwhich an elongated tape is provided with a waterway which extendslongitudinally along the tape and communicates with a series of flowrestrictor channels of tortuous form, at least one of each channelshaving an inlet to the waterway and at least an outlet being providedfrom each channel remote from the inlet to allow the outflow through thetortuous channel.

This general type of irrigation tape is already known, and for instancein Australian Patent No. 516,536 (29122/77) and corresponding U.S. Pat.No. 4,195,784 in the name of Gideon Gilead is shown a tape formed bysuperimposing three foils and marginally dividing together the foils, awater channel being provided between two of the foils while between oneof these foils and a third foil is formed the series of flow restrictedchannels which have communication with the flow channel and with theatmosphere, the inlet and outlet points being displaced in relation toeach other along the flow control channel.

A similar Gilead specification is U.S. Pat. No. 4,175,882 filed Dec. 29,1976, but containing more restricted claims than in the Australiancounterpart.

Similarly the complete specification of Australian Patent ApplicationNo. 34599/76 in the name of Jaime Sahagun-Barragan shows a further formof such tape and relates particularly to a specific form of tortuouspart whereby the flow rate is broken down to allow the tape to act as atrickle feed of water to an area from the waterway of the tape.

The referred to prior art documents are distinguished principally by theposition of the marginal joins of the foils which form the tape.

The specification of U.S. Pat. No. 4,548,360, May 22, 1984, in the nameof Daniel W. C. Delmer uses a single foil doubled back to form a supplytube and overlapped to form a bleed channel between overlapped edges ofthe foil, but the bleed channels results from the overlap.

A recently filed specification by Townsend Controls Pty. Ltd.,Australian Patent Application No. 33361/84, published Mar. 28, 1985,also relates to this type of irrigation tape but relates principally toa particular pattern of the flow restrictor channel and the method bywhich the channels are produced.

In this form a single foil is twice overlapped to form a water channelon one side of a medial portion, a tortuous channel being formed on theother side by embossing.

It is and object of this invention to provide a continuous irrigationtape which is simple to construct and does not require precision layingof adhesives or other connecting elements between the forming foils.

It is a further object to provide a simple and effective method offorming such a tape.

Other objects will be apparent from the following description.

The drip irrigation tape according to the invention is formed from oneor more foils, formed from thermo-plastic material and sealed to producea main waterway extending along the tape, and a series of tortuous flowrestricting channels formed in a portion of the foil which co-operateswith another portion of the foil to close the channels, each channelcommunicating at one position with the main waterway and having anoutlet at another position to give a drip feed from each channel to anarea to be watered.

While the construction can use one or more foils marginally fusedtogether, the preferred method uses a tubular foil or individualsections which can be extruded directly to the tape forming machinewhere it is shaped and manipulated to provide overlapping sections withtwo sections forming the wall of the waterway and another sectioncarrying the flow restricted channels, this section being fused to onewall section.

Features of the invention include a method of folding the vacuum formingmeans for the flow restricting channels, also the temperatures controlsfor fusing, as well as heat flow control, cutting of apertures in thefoils, cutting or nicking an outlet in the restricted channels,controlling the distance between inlet and outlet of each of therestricted channels, and achieving better bonding.

In its finished form the tape of this invention comprises a foil sectioncomprised of a thermo-plastics material which is vacuum formed toprovide a series of tortuous channels which are closed on one side ofthe foil section by a cover foil section fused to the first foil sectionat all meeting areas other than over the channels, ingress of water tothe channels being by a punched aperture for each tortuous channelthrough the central foil section leading to a waterway, and an outletfor each tortuous channel formed by opening a portion of each channel bya cutting away of the vacuum formed channel to allow outflow from thetape, the waterway being formed by a section of foil which extends overthe section of the cover foil which closes the channels and has itsedges marginally fused to the cover foil.

The foil sections which are used can be provided from a tubularextrusion which can be fed directly into a host-forming portion of themachine, and can be cut, folded, manipulated and otherwise directed toform the various necessary foil sections and be rejoined to produce thetape, but the foils can be independently supplied if this is founddesirable, such as by simultaneously extruding the sections and feedinginto the tape-forming machine, the machine comprising means whereby thesections of the foil can be moved forward in the required manner whileone foil section at least is vacuum formed to produce channels andanother foil section is joined thereto to close the channels, a thirdsection being joined to the channel-closing section to form a waterwayleading to the channels through apertures extending from the waterwayinto the channels, apertures being formed at outer parts of the channelto allow slow out-flow for irrigation purposes.

One of the further difficulties relates to punching the aperture foreach tortuous channel through the central foil.

The problem in using a simple punch is that this becomes blunted whereit is used on a continuing basis and this is therefore simply not aviable solution.

A further feature of this invention therefore is to propose a method ofeffecting such an aperture through a sheet of thermo-plastics materialwhich includes pushing against the sheet, a finger, an outermost end ofwhich at least is heated to a temperature which is in excess of themelting temperature of the plastics material.

In preference the shape of the finger is conical with the apex of thecone farthermost from the base adapted to engage against the sheet ofthe plastic and in preference there is a co-operating aperturecoincidentally located on the other side of the sheet which matches thediameter at tis base of the cone shape of the finger.

In preference the conical shape of the finger is such that the apex issubtended by an approximate angle of 90°.

In preference, the temperature to which the finger is raised is suchthat while being above the melting temperature of the plastics material,the temperature will be such that it will effect a reasonably rapidmelting and therefore allowing a retraction of the plastic surroundingthe point of entry by reason of such first piercing and subsequentheating.

In preference, the finger and the co-operating aperture are supported byparallel rollers between which the foil comprised of the thermo-plasticsmaterial passes and there are activating means causing the respectiverollers to rotate causing coincident motion effecting a piercing whichis co-ordinated with a relative location of a vacuum forming drum.

One of the next problems relates to cutting an aperture as an outlet foreach tortuous channel.

A number of different techniques have been tried over the years but ithas become clear that these are either too expensive causing inefficientmanufacturing operations or they do not provide on a continuing basis areliable opening as an outlet.

According to a further preferred feature then there is provided that foreach tortuous channel, there is an outlet part which is offset to a sideas compared to a remaining part of a respective tortuous channel andthere are means comprising a heated blade fixedly located so as toensnare such offset part of the tortuous channel solely, as the tortuouschannel passes a nicking station.

In preference, the nicking station includes a blade having a broad face,and the temperature being held above a melting point of thethermo-plastics material so that the effect can be to push the plasticsmaterial away from a then effected aperture which is adapted to act asan outlet for a respective channel.

Such an arrangement overcomes a further problem in which there might bea channel part raised higher than that providing the remaining tortuouspath, the difficulty here being that when the tape is subsequentlyfolded for storage purposes, the effect will be to compress some of theremaining thermo-plastics material on the outlet part hence causing thisto unnecessarily close and destroying the effect.

By in fact having the outlet to a side, surrounding tape is to a verylarge extent held separate from the outlet by the remaining channel partof the tape.

A further problem that has been found to occur relates to achieving ajoining together of two thermo-plastics sheets in such a way that therewill be effected a substantially strong bond sufficient to withholdunder significant irrigation pressures and to achieve this simply byeffecting a first surface melting of the plastics material and thenforcing these together.

Our experience hitherto has been that this has been very difficult toachieve.

While at first it might appear to be simple in practice, it was foundthat despite significant melting and significant pressures, there tendedto be very large areas beneath the surface which had not adhered andthere seemed to be no consistency in establishing why some parts werewelding and others were not.

After substantial experimentation, it has been discovered that effectiveadhesion can be achieved if there are provided distributed points ofsignificantly higher pressure during the bringing together of the twosheets to be adhered.

In a simple way, this required providing a so-called dimpled or knurledroller to effect the application of pressure with the distribution ofpressure points being sufficiently small so as not to cause difficultywith the application but nonetheless adequately dispersed for thepurposes.

The reason for this being effective is not entirely clear but it issuspected that with applying distributed pressure points, this leavesvalleys between the pressure points in which vapor can gather whichwould otherwise be encaptured between a broader sheet face, andfurthermore, there would tend to be a more concentrated transfer of heatthrough the actual transfer point leading to a greater local heatingwithout losing total integrity of the tape.

It is finally to be noted in the stated manufacture of tape of this typeusing thermo-plastics material, that the tape itself while being heatednonetheless is also so used to support itself between rollers.

The effect therefore of heating on such a tape has to be such that whilethere would be caused a surface heating, the tape will not have beenheated to the extent that all the tape will have reached a melttemperature before it is either fully supported by other means or cooledappropriately.

In order however that the invention may be more fully appreciated, someembodiments thereof will not be described with reference to theaccompanying drawings which are of a diagrammatic nature only andintended to give a general idea of the embodiments of the invention butare not be taken as limiting the invention to the embodiments shown.

In the drawings:

FIG. 1 is a schematic block diagram to show the stages by which theirrigation tape is formed and the method of production,

FIG. 2 is a schematic view of the machine which forms the tape from atube of plastic material which may be produced and processed by themachine the subject of this invention,

FIG. 3 shows diagrammatically stages in the production of the tape froma tube of plastics material,

FIG. 4 is a view similar to FIG. 2 but showing the tape produced fromflat foil sections,

FIG. 5 shows schematically the final assembly of the foil sections inthe completed tape, and

FIG. 6 shows how multiple tapes can be simultaneously formed and thefoil then split to form a plurality of tapes,

FIG. 7 is a schematic view of the arrangement by which punched aperturescan be effected and how these can be caused to cut in co-ordination withthe position of a main vacuum drum,

FIG. 8 is a detail of the projecting finger and appropriate receivingaperture,

FIG. 9 is a view from an end showing two rollers in parallel andproviding for four apertures to be cut in line across the width of thetape if this is the type of tape to be used,

FIG. 10 is a plan view of a section of tape thus formed showing indotted outline an inlet aperture through a central foil section andthere being indicated a general useful range of positions over which theaperture can be located, also showing outlets offset to one side of theremaining channel and showing in dotted outline the position of acutting tool which can be left in a fixed position and which will effecta nicking of such a channel part casing an outlet,

FIG. 11 is an enlargement of an outlet part of such a view as in FIG.10,

FIG. 12 is a side view of the nicking blade including its shape andposition relative to the channel on the tape as it is passing over aroller, and

FIG. 13 illustrates the manner in which the foil section is caused to bedimpled as it is brought in contact after substantial melting of a coverfoil section as it is caused to be pressed against the foil sectioncarrying the plurality of vacuum formed channels.

Referring to the drawing shown in FIG. 1 which depicts the generalconstruction of the invention, it will be noted that a foil supply 1 isindicated which may produce either a tubular foil to be later slittedand otherwise treated or may supply individual foils for two or three ofthe members which go to make up the invention, the foil from the supplygoing to a foil separation station 2 where the necessary foilconfigurations are produced, a first oil section 3, referred to as thechannel-forming foil section, passing to a feed station 4 from which thefoil is fed for further processing. This channel forming foil section 3is cut from a tubular foil as will be described later herein withreference to FIGS. 2 and 3 but the sections can be separately extrudedas shown in FIG. 4.

Another foil section 5 is used to cover the channel-forming foil section3, and a third foil section 6, referred to as the waterway formingsection, is disposed adjacent to the cover foil section 5.

From the channel foil feed station 4 the channel-forming foil section 3passes through a pre-heating station 8 to the vacuum forming and heatjoining station 9 in which the foil after being pre-heated is furtherheated and when in a sufficient ductile state passes over a vacuum drumhaving the channels formed therein so that the foil is vacuum formed atthis locality and is in readiness for the next stage of production whichis also carried out on the vacuum drum and which consists in joining itto the cover foil section which is fused to it in all areas excepting atthe channels to form closure means for the channels. This will laterherein be described with reference to FIGS. 2 and 4.

The cover foil section 5 and the waterway forming section 6 are fed fromthe cover and waterway feed station 10 to a cover foil punching station11 in which a series of holes 11a are punched in the foil at appropriatelocations.

The location of the hole or aperture 11a is governed by a controlactivated in association with the vacuum drum which automaticallyactivates the punching station 11 when a selected part of each channelpasses a given location.

In this way, the location of the aperture 11a with respect to the outlet16f, controls the length of the tortuous pathway or restricted path thatthe water will have to travel in order to be released to atmosphere.

Self-evidently, the shorter this distance, more water will flow whereasthe longer distance as is shown in FIG. 13, will achieve a maximumpressure reduction effect.

One of the features of being able to pack so much distance in a tape, isto ensure that the actual aperture size formed between the channel andthe cover foil will be able to be reasonably large but providing anadequate pressure radiation.

One feature of importance is that the diameter of the aperture 11ashould be such as to encompass at least several of the channels or moreparticularly the legs in the adjacent channels so that the specificlocation of the aperture will not have to coincide with one part of achannel precisely.

It is of little consequence that it strikes across two or three legs ofa channel in that it will obviously allow the water to take the shortestpath.

It is also self-evident that the aperture while being shown in dottedoutline as round is not quite so round in practice. Accordingly,allowing for changes in shape of the hole means that the aperture sizehas to be this little bit larger.

These register with a respective channel when the cover foil section ispassed through a pre-heating station 12 and then joins the channelforming foil section 3 on the vacuum forming drum where the joiningtakes place by fusion of the channel forming foil 3 and the cover foil5, fusion taking place over the complete area excepting over thechannels in the channel forming foil section 3. This is assisted howeverby a dimpling or knurling of a pressure roller as shown particularly inFIG. 13.

The waterway forming foil section 6 bypasses the area where thecover-forming foil 5 is punched as shown in FIG. 1 but rejoins the coverfoil section 5 and passes over the drum as the outer foil section 6 andis not bonded to the cover foil section 5 but the three foil sectionsthen passes to an edge fusing station 13 where the marginal edges of thesecond and third foil sections, that is the cover foil section 5 and thewaterway forming foil section 6 are fused together.

From the edge fusing station 13 the tape now goes to the channel nickingstation 14 shown particularly at FIGS. 10, 11 and 12 in which an offsetend of each channel is nicked away by a heated blade 16.

This is achieved by using a flat fronted blade the typical outline beingshown at 16a and the front edge 16b being located so as to ensnare theoutlet part 16c of the channel.

The blade 16 is in the form of an electrode coupled between electrodeconnections 16d and 16e so that the temperature can be controlledthrough appropriate Thyrister control means by controlling the amount ofcurrent passing through the blade 16.

The temperature of course is governed by the extent to which there isneeded to be a heating and melting effect of the selected plasticsmaterial.

Nonetheless, he point is that the outlet channel part 16c has a heightthat is substantially the same as the remaining channel and the outletis offset to one side of the remaining channel in each of a series ofchannels so that the location of the blade 16 can be fixed and cantherefore cut automatically by nicking and in fact pushing away themelted material as it passes over the outlet channel part 16c. From thisstation the tape goes to a trimming station 15 where the tape iscompleted.

Referring now particularly to FIGS. 2 and 3 which show the form of theinvention when a tubular foil is processed to produce a tape.

The form of the foil is particularly shown at the various stations inFIG. 3 and it will be noted that at station A the foil is of tubularform, station B being the foil separation station at which the foil iscut to form two sections, the cut being made at about one third thedistance in from one end of the folded foil and the two parts of thefoil are then separated with the channel-forming foil 3 passing to thechannel foil feed station 4 and from thence to the pre-heating station 8from which it is taken to the vacuum forming and sealing station 9 whereit passes around a rotating drum 20 on which it meets the other twofoils namely the cover and waterway foils.

FIG. 3A shows the tubular foil and B shows the channel-forming foil 3 inits still folded position but with the doubled back portion adjacent toit forming the cover foil section 5 and the waterway foil section 6.

The channel-forming foil section 3 is opened out into a planar formbefore it reaches the feed station 4 where it is gripped between rollers21 and driven forward and then passes through the pre-heating station 8where both sides of the foil are raised in temperature, the pre-heatedfoil then passing around a roller 22 to be deposited on the drum 20where it is further heated by the heating members 23 and is then carriedto a heater 24 where its surface is brought to the required fusingtemperature.

The foil sections 5 and 6 pass between a pair of rollers 25 and are thenseparated slightly so that the foil section 5 can be punched atappropriate localities in the cover foil punching station 11, and thisfoil is then pre-heated at 26 and together with the waterway formingfoil 6 is laid onto the channel forming foil 3 by a pressure roller 27.

At this point the outer surface of the channel forming foil 3 and theouter surface of the cover foil 5, which is disposed at the back of thewaterway forming foil, are fused together because the two surfaces havebeen raised to the required temperature but as the waterway forming foil6 is on the outside of the laminate now positioned on the drum 20 it isnot joined to the foil with which it is in contact.

The foil sections, as a laminate, then continue around with the drum 20through a cooling zone 28, the drum 20 being water cooled and the drumpreferably consisting of a series of tiles 29 which extend across thedrum and which are themselves channelled with the channels communicatingthrough apertures with the inside of the drum 20 which is held atreduced pressure so that the channel-forming foil section 3 is patternedby sections of it being drawn into the channels of the drum andimmediately the cover foil section has been joined to it by fusion dueto the heating of the two surfaces which are pressed together, coolingis applied to the area of the drum which then continues until the nowpartially completed tape is taken from the drum around a roller 30 atwhich is situated a nicking member 31 which notches out appropriate endportions of the channel to allow flow from the channels to theatmosphere.

From this the tape continues to the edge fusing station 13 whereappropriate edges are fused together, which edging will be clear fromFIGS. 5 and 6 which show a preferred form of construction, FIG. 5showing how a single tape is formed, but FIG. 6 showing how a relativelywide compound tape can be formed which is then slitted in the trimmingstation 15 by cutting through the marginal areas of the tapes at theposition indicated by 32 in FIG. 6.

Where such a compound tape is formed it will be realised that, referringto FIG. 3, the width of the tape sections 3, 5 and 6 are sufficient tocover the area of a compound tape but as stated the tapes can be formedas a multiple production system where a series of tapes are formed sideby side and then split to form individual tapes.

Referring now more particularly to FIG. 4 in which similar numbers havebeen used for corresponding parts, the system involved there usesseparate foils rather than sections of a wider foil which can either bepreformed or can be extruded directly into the forming machine with thefoil sections disposed preferably as shown in FIG. 6.

While features of the invention can be substantially varied some detailsregarding temperatures and mechanisms will now be referred to.

During manufacture of the tape the foil being a thermo-plastics materialis fed through the driven rollers 21 in the feed station 4 and then bothsides are heated to an even temperature by radiant heaters in thepre-heating station 8. It is preferably to feed through the drivenrollers 21 so as to eliminate tension in the foil as it passes throughthe radiant heaters in the station 8 the temperature not being too highhowever to allow undue stretching under tension.

Foil surface temperatures, sensed by temperature sensing means, haveproved that the correct temperature should be in the vicinity of 60° C.with the thermo-plastics materials normally used for these tapes, whichtemperature is preferably maintained by Thyrister control and electronicmonitoring means.

After pre-heating, the foil passes round the roller 22 which is distantfrom the main drum 20 by the thickness of the foil and this roller 22,which is also heated, positions the channel-forming foil sectioncorrectly on the vacuum drum 20 without inducing unnecesary stress inthe material, the roller 22 being maintained at a constant temperatureof approximately 100° C. The tension on the foil section 3 can beaccurately controlled by the rollers 21 and the rate of rotation of thedrum 20.

The channel-forming foil section 3 is now heated externally from thedrum over a relatively long circumferential section of the drum 20,which is also heated, so as to regulate the temperature of the foil bythe radiant heater 23 to just above permanent deformation temperature,the internally exerted vacuum drawing the heated foil into the channelsof the drum 20, and the temperature of the foil is then reduced belowdeformation temperature before leaving the embossed face of the drum,this being achieved by maintaining the drum 20 at about 50° C. throughinternal water cooling.

The tiles which form the drum 20 have a large number of vacuumtransferring holes radially through the tiles which are connected by aseries of cross holes to supply means through the hollow shaft of thedrum 20 in any approved manner.

The cover foil section 5 and the waterway forming section 6 of the foilare heated to approximately 90° C. by radiant heaters 26 and cometogether with the channel-forming foil section 3 and at the point ofmeeting the mating faces of the foils 3 and 5 are elevated to above melttemperature by the radiant heaters 24, this heating occurring just priorto the two surfaces being pressed together between the drum 20 and thepressure roller 27 so that the two surfaces fuse together due to thepressure exerted by the drum 20 and roller 27 at all points exceptingwhere the channels occur, this bonding taking place only between thechannel-forming section 3 and the cover foil section 5, there being nobonding of the waterway forming section 6 to the cover foil section 5.Due to the rotation of the drum the relatively complete but not edgebonded sections of the foil laminate move around the drum 20 to theroller 30, the reason for the foil extending almost completely aroundthe drum 20 being to form a vacuum seal so that the vacuum can bemaintained within the drum.

The face of the drum 20 and/or the roller 22 is patterned to provide amultiplicity of small dimples on the foil section 3 for better bondingto the cover foil section 5.

The foil laminate now passes through the nicking station 14 to open tothe atmosphere projecting the channels at appropriate locations such asat the edges, communication between the waterway and the channels havingbeen provided by the apertures at the cover foil punching station 11.

The means for punching the cover foil section 5 comprise a drum 32having punches 33 of somewhat conical shape on the surface whichco-operate with a roller 34 having corresponding recesses 35, but thetemperature of the punching members is maintained such that the materialwhich is to be removed is at least partly vaporised and causes thematerial to shrink away from the centre of the perforation to provide anaperture of the required dimension, the drum 32 carrying the punches 33being synchronised with the movement of the foil section 5 to ensurethat when the cover foil registers with the channels in thechannel-forming foil section 3 these apertures are correctly registeredin relation to the part of each channel where ingress of water from thewaterway is to occur.

From the nicking device 31 the foils pass through an edge sealingstation 13 where radiant heater means, positioned on each side of thecompound foil, direct sufficient heat to both sides of the tape alongnarrow lines to bond the edges of the cover foil section 5 of the tapeto the waterway forming sections 6 of the tape to form as it were a hoseopening to the channels so that flow can then take place through thechannels in which flow is restricted to allow slow outflow from the endsof the channels where the material has been nicked away.

After so marginally bonding, the marginal edges of the tape are trimmedin the trimming station 15, this trimming being unnecessary in the caseof the manufacture of a single length of tape but being essential wherea series of such tapes are formed side by side from relatively wide foilsections as shown in FIG. 6. The marginal bonds between the cover foilsection 5 and the waterway foil section 6 are designated 34.

With this invention the channel-forming section 3 of the tape is bondedto the cover foil section 5 of the tape over its complete width and noedge bonding of this occurs but the waterway is formed by bonding theextending edges of the wider cover foil section 5 of the tape to themarginal edges of the water foil 6, thus allowing the waterway to be ofsubstantial width to feed a number of restrictor channels disposed alongthe finished tape and arranged in zig-zag fashion as shown but this formof channel is not necessarily essential as any relatively long channelswith flow restrictor means in them can be used.

I claim:
 1. A method of manufactured of drip irrigation tape comprisinga plurality of longitudinally extending foil sections formed fromthermo-plastic material and sealed to form a longitudinally extendingmain waterway and a plurality of tortuous flow restricting channels incommunication with said main waterway, said main waterway having aninlet for receiving irrigation water and each of said channels having anoutlet for discharging said irrigation water, said plurality of foilscomprising first, second and third foils wherein said second and thirdfoils form said waterway and said first and second foils form saidchannels, said method comprising;(a) preheating said first foil section,(b) introducing the preheated first foil section onto a rotating channelforming drum having impressed therein a series of channel shapes aroundthe circumference of the drum and including apertures from the channelshape to vacuum applying means, said channel shapes forming said seriesof flow restricting channels, (c) subjecting the foil to further radiantheating to raise its temperature above a melt point when it is beingsupported by the surface of the drum, (d) effecting a drawing in to thechannel shape of appropriate parts of the thus heated foil, (e)effecting a radiant heating of an outermost surface of the said firstfoil and an inner surface of said second foil as it is introduced ontothe said first foil on the respective thermo-plastics material comprisedin the respective foils, and then (f) effecting through a pressureroller, a joining pressure to join the said foils whereby to effect aclosing over of the respective channel shapes in the first said foil,said method being further characterized in that said channels haveoutlet parts which are disposed closer to an edge of said first foilsection than the remaining parts of said channels and wherein saidoutlets are formed by cutting said outlet parts with a heated bladepositioned close to said outlet parts as said tape passes by, saidcutting taking place subsequent to the tape being moved from the channelforming drum.
 2. A method of manufacture of a drip irrigation tape as inclaim 1 further characterised in that the pressure roller has aplurality of dimples around its circumference whereby to effect suchpressure over spaced apart locations.
 3. A method of manufacture of anirrigation tape as in claim 2 in which there are hole punching meanseffecting a punching of the said second foil prior to it being directedinto adjoining relationship with said first foil.
 4. A method ofmanufacture of an irrigation tape as in claim 3 further characterised insaid hole punching means comprise a finger which is heated to atemperature above the melting temperature of the thermo-plasticsmaterial from which said second foil is formed.
 5. A method ofmanufacture of a drip irrigation tape as in claim 4 furthercharacterised in that the finger is located on the surface of a firstdrum and there is a second drum located on the opposite side of the tapewith a correspondingly located aperture and there are means to effectsynchronous rotation of the respective drums whereby to provide uponinitiation coincident full turn rotation matching the speed of the tapepassing between the said drum.
 6. A method of manufacture of dripirrigation tape as in claim 5 in which the hole punching means iseffected by means associated with the channel forming drum.
 7. A methodof manufacture of drip irrigation tape as in claim 1 furthercharacterised in that the plurality of longitudinally extending foilsections are formed from a tubular extrusion of plastics material, saidtubular extrusion being fed through a separating and re-forming station,to produce said first, second and third foils.
 8. A method ofmanufacture of a drip irrigation tape as in claim 1 in which the tapeforming the waterway which comprises the said second foil and said thirdfoil are constituted as being the same integral part of a first extrudedfoil and in which subsequent to a first part of the second foil beingadhered over all meeting areas to the said first foil, a remaining partof the said second foil is folded across so as to have a weld along themeeting edge providing thereby the main waterway.
 9. A drip irrigationtape comprising a plurality of longitudinally extending foil sectionswhich together define a longitudinally extending main waterway having aninlet for receiving irrigation water and a plurality of tortuouschannels in communication with said main waterway, each of said channelshaving an outlet for discharge of irrigation water;said plurality offoil sections including first, second and third foil sections which arejoined together, at least said first section being formed ofthermoplastic material, said second and third foil sections togetherforming said waterway and said first and second foil sections togetherforming said channels, said channels being formed in a portion of saidfirst foil section, the remaining portion of said first foil sectionbeing fused to said second foil section to enclose said channels; eachof said channels comprising a plurality of interconnected legs whichtogether define a flow restricting path for water, each of said channelsfurther including an inlet and an outlet part which is remote from saidinlet, said outlet being formed in said outlet part, said inlet being anaperture in said second foil section extending across several of saidlegs and providing communication between said channel and said waterway.10. A drip irrigation tape as in claim 9 in which each tortuous channelhas an outlet part which is offset to a side as compared to theremaining part of said tortuous channel, the outlet being formed by acutting away of a portion of such outlet part.
 11. A drip irrigationtape as in claim 9 in which each of said legs has a zig-zagconfiguration.
 12. A drip irrigation tape as in claim 9 in which saidlegs extend transversely and said legs have ends which arelongitudinally aligned and spaced from the edge of said first foilsection and in which the outlet parts of said channels are offset to theside compared to the remaining parts of said channels.
 13. A dripirrigation tape as in claim 9 in which all of said foil sections areformed of thermoplastic materials.
 14. Apparatus for the manufacture ofa drip irrigation tape comprising a plurality of longitudinallyextending foil sections formed from thermoplastic material and sealed toform a longitudinally extending main waterway and a plurality oftortuous flow restricting channels in communication with said mainwaterway, said main waterway having an inlet for receiving irrigationwater and each of said channels having and outlet for dischargingirrigation water, said plurality of foils comprising first, second andthird foils wherein said second and third foils form said waterway andsaid first and second foils form said channels, the said apparatuscomprising,(a) a channel forming drum, said drum including a pluralityof shapes for forming channels in said first foil, said channels shapesbeing impressed with an externally impressed peripheral shapes aroundthe drum and a plurality of apertures providing for passage of air fromwithin each channel shape to an internal vacuum applying means; (b)means for supplying said first, second and third foils to said channelforming drum; (c) preheating means for preheating at least said firstand second foils before they are introduced onto said drum; (d) heatingmeans for heating said first foil as it passes over said drum to causefusion and channel formation; (e) means for applying said second andthird foils to said drum after said channels have been formed in saidfirst channel and for fusing said second foil to all portions of saidfoil except for the portion which forms said channels; (f) cooling meansfor cooling parts of the periphery of channel forming drum; (g) meansfor forming apertures in said second foil so as to provide communicationbetween said waterway and said channels and (h) means for slitting saidfirst foil in the vicinity of the outlet parts of said channels so as toprovide outlets for said channels.
 15. Apparatus for the manufacture ofa drip irrigation tape as in claim 14 wherein each of said foils iscomprised of thermo-plastics material and wherein said heating means forheating said foil as ti passes over said drum are radient heating means,said apparatus further including means to effect by application of aheated finger, apertures within said second foil, means to continuouslymonitor the temperature of any such applied radiant heating and tocontrol this whereby to maintain a constant being effect of such radiantheating means, and a pressure applying roller having dimples around anexternal surface thereof whereby to effect pressure through spaced apartlocation effected by the dimples whereby to cause a joining together ofa respective first and second foil in which the first foil has hadformed therein a channel shape and being drawn into a channel shapedmould by vacuum applying means, and the second foil has been introducedagainst an external surface of this first foil.
 16. Apparatus for themanufacture of drip irrigation tape as in claim 15 in which said meansfor slitting said first foil comprises an outlet nicking station whichcomprises a heated blade having a wide frontal part adapted to form anoutlet opening in the outlet part of each channel.
 17. Apparatus as inclaim 14, in which each of said channels of said tape has an outlet partwhich includes said outlet said is offset to a side as compared to theremaining part of said channel, and said nicking station is positionedso as to slit said outlet part and thereby form said outlet withoutcutting the remaining part of said channel, said nicking station beinglocated so that said tape passes by said nicking station after it hasleft said channel forming drum.
 18. Apparatus for the manufacture ofdrip irrigation tape as in claim 14, further including an edge sealingstation comprising radiant heater means for bonding the edges of saidthird foil section to said second foil section, said edge sealingstation being located so that said tape passes said edge sealing stationafter it has passed said slitting station.